1. Field of the Invention
The present invention relates to structure of a magnetic recording/reproducing apparatus having a torque generating function providing the most appropriate torque required when cassette tape is running at a constant speed and at a high speed, respectively.
Furthermore, the present invention relates to structure of magnetic recording/reproducing apparatus having a function of determining a taking-up state and a taking-up finish state of cassette tape.
2. Description of the Background Art
Generally, in a magnetic recording/reproducing apparatus, when a tape is running at a constant speed in recording/reproducing, a reel stand taking up the tape is rotated with relatively low torque (in a compact cassette, generally about 35 g.cm), and when the tape is running at a high speed such as in fast forwarding/rewinding, the reel stand is rotated for taking up with relatively high torque (in a compact cassette, generally about 70-100 g.cm). Accordingly, a low torque generating mechanism and a high torque generating mechanism are individually provided in an apparatus, and the constant speed running and the high speed running of cassette tape have been implemented by transmitting torque generated by each mechanism to a predetermined reel stand.
In such a tape running mechanism, however, the number of parts is large and the loss of space is great, which makes it difficult to make apparatus smaller and to reduce manufacturing cost.
Magnetic recording/reproducing apparatus which solves such disadvantages include one disclosed in Japanese Utility Model Publication No. 2-6519. In the magnetic recording/reproducing apparatus, structure is disclosed in which generating means for low torque and generating means for high torque are provided on the same axis. FIG. 21 is a plan structural view of a magnetic recording/reproducing apparatus disclosed in the published application, and FIG. 22 is a cross sectional structural view of the reel stand driving mechanism shown in FIG. 21. A conventional magnetic recording/reproducing apparatus includes a driving motor 102, a pulley 122 to which the rotation force of the motor is transmitted through belt 120, a supply reel stand 103 and a take-up reel stand 104 engaging with cassette tape, and a reel stand driving mechanism for transmitting the rotation force transmitted to the pulley 122 to a predetermined supply reel stand 103 or take-up reel stand 104. The reel stand driving mechanism includes an intermediate gear 123 and a driving gear 125 provided on the same axis as pulley 122. A first sliding clutch 124 is interposed between pulley 122 and intermediate gear 123, and a second sliding clutch 126 is provided between intermediate gear 123 and driving gear 125. The driving gear 125 and the intermediate gear 123 are pressed onto pulley 122 by a spring 127 through the first and second sliding clutches 124, 126.
In operation, in the constant running of tape requiring low torque, the rotation force of pulley 122 is reduced to predetermined low torque through first sliding clutch 124 and second sliding clutch 126, and then transmitted to the take-up reel stand 104 side by driving gear 125. When the tape is running at a high speed requiring high torque, the rotation force of pulley 122 is slightly reduced and transmitted to an intermediate gear 123 through first sliding clutch 124, and furthermore transmitted to take-up reel stand 104 or supply reel stand 103 through a pivoting gear 129. The pivoting gear 129 then simultaneously engages with intermediate gear 123 and driving gear 125. The second sliding clutch 126 is thus fixed not to function.
A conventional magnetic recording/reproducing apparatus, however, has the following problems.
(1) Firstly, it is difficult to set a value of high torque extracted from pivoting gear 129 and a value of low torque extracted from driving gear 125 at the most appropriate values, respectively. This comes from the structure in which first sliding clutch 124 and second sliding clutch 126 are pressed by a single compression spring 127. That is to say, in first and second sliding clutches 124 and 126, felt which is generally formed of wool or the like is sandwiched between two rotating bodies, which is pressed by a spring in one direction to transmit desired torque by the sliding friction. Accordingly, the transmitted torque is affected by a friction factor between the two rotating bodies and the felt, and the compressive force supplied to the two rotating bodies. The friction factor between the two rotating bodies and the felt has a large variety, which is largely affected by the environments, especially by humidity. Accordingly, it is necessary to precisely set the load of the compression spring in setting transmission torque. However, it is difficult when compressing two sliding clutches 124 and 126 with a single compression spring 127 as described above to make setting so that the most appropriate compressive force is applied to each. Accordingly, in a conventional structure, it has been difficult to set values of both of high and low torque at the most appropriate values.
(2) Secondly, in order to obtain high torque, it must be extracted through first sliding clutch 124 from pulley 122 through pivoting gear 129 which simultaneously meshes with intermediate gear 123 and driving gear 125. Pivoting gear 129 must be simultaneously brought into mesh with intermediate gear 123 and driving gear 125 from a separated condition. If intermediate gear 123 and driving gear 125 are in alignment, the mesh can be smoothly made, but if they are not in alignment, pivoting gear 129 must be pressed so that either one of the gears is relatively moved to bring tooth surfaces of the two gears in alignment. However, second sliding clutch 126 having friction force is interposed between intermediate gear 123 and driving gear 125. Accordingly, for bringing pivoting gear 129 into mesh with both gears, it must be pressed with force which overcomes the friction force of second sliding clutch 126. Accordingly, if it is made to obtain the pivoting force for pivoting gear 129 utilizing the rotation force from the driving motor, the motor is required for high driving force, resulting in an increase in cost. Also, when the mesh is not made smoothly because of such conditions as described above when pivoting gear 129 is brought into mesh, abnormal sounds such as gear noise may occur.
A conventional magnetic recording/reproducing apparatus has an auto stop function of detecting a tape take up finish state of cassette tape and automatically stopping a motor which drives reels. FIG. 23 is a plan structural schematic view showing structure of a tape driving portion of a conventional magnetic recording/reproducing apparatus, FIG. 24 is a sectional structure diagram taking along the cut line E--E in FIG. 23, and FIG. 25 is a plan structure schematic view taking along the arrow F--F of FIG. 24. FIG. 23 and FIG. 25 are a top view and a bottom view with respect to each other. Referring to FIGS. 23 through 25, with a cassette 75 attached, it engages with two reel stands 76 and 77. Magnetic tape of cassette 75 is provided so that it passes between one capstan 78 and a pinch roller 80 and between the other capstan 79 and pinch roller 81. The shown magnetic recording/reproducing apparatus has a driving mechanism capable of constant running in a forward direction and constant running in a reverse direction. In running at a constant speed in the forward direction, the tape is sandwiched and held between capstan 78 and pinch roller 80, which is fed in a normal direction "a" with take up rotation operation of a FOR reel stand 76 in the normal direction X and the constant speed rotation operation of capstan 78 and pinch roller 80.
In reverse direction constant speed running, the magnetic tape is sandwiched and held between capstan 79 and pinch roller 81, which is fed in the reverse direction "b" with the reverse direction rotation Y of a REV reel stand 77 and the constant speed reverse direction rotation of capstan 79 and pinch roller 81.
A conventional magnetic recording/reproducing apparatus has an automatic stop mechanism for automatically stopping operation of the apparatus when a terminal end of the tape in run is reached. The detecting mechanism for detecting the terminal end of tape has structure as described below. First, a reflection panel 70 is provided on the same axis as that for FOR reel stand 76. As shown in FIG. 25, in reflection panel 70, portions with high optical reflectance ratio and portions with low reflectance are alternately arranged for every constant angle around the rotation axis. A light emitting light receiving element 71 is provided at a position facing rotation panel 70. Furthermore, a rotation detecting device for electrically detecting rotation operation of rotation panel 70 is connected to light emitting light receiving element 71.
FIG. 26 is a schematic diagram showing positional relationship between rotation panel 70 and light emitting light receiving element 71, and FIG. 27 is a block diagram for describing a rotation detecting device for detecting the rotation movement of rotation panel 70. Light emitting light receiving element 71 emits light to the rotating panel and receives light reflected from reflection panel 70 to convert its magnitude into an electrical signal. A frequency/voltage converter 72 converts the frequency of a periodical signal supplied from light emitting light receiving element 71 into voltage to output an output voltage v.sub.1. A comparator 73 receives the output voltage v.sub.1 from frequency/voltage converter 72, compares it with an output voltage v.sub.0 which is outputted from frequency/voltage converter 72 in the case where the frequency of a signal outputted from light emitting light receiving element 71 is 0, and if v.sub.1 -v.sub.0 &lt;0, outputs High, and if v.sub.1 -v.sub.0 =0, outputs Low. Furthermore, a tape take up determining device 74 receives the output of comparator 73, and makes a determination that the tape is being taken up if the output is High and that taking up of the tape is finished if the output is Low. Then, when a determination is made by tape take up determining device 74 that the tape has been taken up, the rotation of the driving motor is stopped.
However, in such a mechanism for detecting tape take up states as described above, there has been a problem that a case may occur in which the automatic stop mechanism does not operate in spite of a fact that the tape run should be stopped. It is described referring to FIGS. 28 and 29. FIG. 28 is a schematic diagram of the normal direction tape drive indicating operation conditions of the tape driving system in the normal direction constant run and FIG. 29 is a schematic diagram of the reverse direction tape drive.
First, referring to FIG. 28, in the forward direction constant run, the tape is fed from the REV reel stand 77 side to the FOR reel stand 76 side at a constant speed by FOR reel stand 76 always rotating in the X direction, capstan 78 feeding magnetic tape in the same direction and pinch roller 80, which is taken up by the reel of cassette tape 75 engaging with FOR reel stand 76. Imagine a case where the rotation of FOR reel stand 76 is stopped due to some abnormality in the forward direction constant speed run. In this case, capstan 78 continues to feed the tape in the forward direction in order to maintain the rotational movement. On the other hand, when the rotation of FOR reel stand 76 is stopped, the rotation of reflection panel 70 coaxially provided is also stopped. Then, the above-described rotation detecting means determines that the tape has been taken up, and then the automatic stop mechanism operates to stop the driving motor. The rotation operation of capstan 78 thus stops, too.
Referring to FIG. 29, however, in the reverse direction constant speed run, a normal stopping operation is not carried out as in the forward direction run. That is to say, in the reverse direction constant speed run, REV reel stand 77 rotates in the Y direction and the tape is fed at a constant speed in the same direction by capstan 79 and pinch roller 81. The magnetic tape is thus taken up at a constant speed from the reel side engaging with FOR reel stand 76 to the reel side engaging with REV reel stand 77.
Imagine that the rotation of REV reel stand 77 is stopped due to some abnormality. Capstan 79 and pinch roller 81 maintains the rotational movement even when the rotation of REV reel stand 77 stops, to continuously forwarding the magnetic tape. Then, FOR reel stand 76 also maintains the rotation movement with the tape feeding operation of the capstan 79 and pinch roller 81. Accordingly, reflection panel 70 provided in FOR reel stand 76 still maintains the rotating state. Therefore, the rotation detecting device makes a determination that the tape is being taken up not to operate the automatic stop mechanism. Accordingly, the magnetic tape fed by capstan 79 and pinch roller 81 is continuously fed out toward the reel engaging with REV reel stand 77, with the result that the magnetic tape is continuously pulled out from cassette tape 75. In this case, a problem occurs in which the magnetic tape is damaged to be unusable.